This invention relates generally to electrical conductors, and more specifically relates to an electrically conductive cable assembly, which is especially adaptable to use as an ignition cable for internal combustion engines or the like.
The ignition cables which are conventionally utilized with internal combustion engines, most commonly comprise a central electrically conductive core which is surrounded by an elastomeric electrical insulator such as a natural or synthetic rubber or other synthetic elastomer having good insulating properties and relatively good resistance to heat and the adverse chemical environment present in the vicinity of the said engine.
The central conductive core of the ignition cable has most commonly comprised a metallic conductor, which often takes the form of stranded copper or so forth. It has, however, also been known for many years to utilize non-metallic current-carrying conductors enclosed in insulating jackets or the like. It has further, long been recognized that certain types of such non-metallic conductors display distributed resistance characteristics, and in consequence, serve to reduce RF and other high frequency electrical disturbances which often emanate from the simple metallic conductor type of cable. Such electrical emanations can present a most serious interference problem with regard to operation of radio and television sets, or with respect to operation of other communication equipment.
Over the years, various types of non-metallic current carrying cores have been proposed. British Pat. No. 464,278, for example, which was published in 1937, discloses an ignition cable comprising an outer cover of rubber or other flexible insulation material, and a flexible core of non-conducting fibrous material which has been coated or impregnated with a conductive medium in a finely divided condition. For the fibrous core, a stranded silk, cotton or linen thread may be employed. This thread can be impregnated with colloidal graphite. A similar concept is disclosed in British Pat. No. 547,481.
More recently, high frequency noise prevention cables for ignition applications have been proposed which employ non-metallic filaments in the conducting core of the cable. Such filament can, for example, be formed from glass, with the glass filaments being provided with a film of conductive non-metallic particles such as of carbon, or graphite, which is dispersed in a binding agent. An assembly of this type is discussed in U.S. Pat. No. 3,683,309.
It is also known, as for example is disclosed in U.S. Pat. No. 3,870,987, for the central conductive core in an automobile ignition cable to comprise a plurality of graphite-impregnated fiberglass filaments.
While many of these structures have indeed represented useful and practical improvements in the pertinent art, the said cable constructions have suffered from a variety of problems. Among other things, the non-metallic conductive core members as above discussed, have in many instances been lacking in flexibility, and have exhibited poor strength. Further, the electrical properties of these non-metallic materials have in many instances been erratic. This is often due to the fact that in most instances, electrical conduction is actually effected via dispersed discrete particles. The conductivity of the said materials further, is in many instances too low to be fully adequate for modern automobile ignition systems; and in addition, many of the prior art cable constructions do not stand up to the prolonged high temperature and corrosive environments existing in the vicinity of modern engines.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide an automobile ignition cable structure or assembly, which has excellent and uniform electrical conductivity characteristics, which displays high tensile strength properties, which may be repeatedly and readily flexed without producing physical or electrical damage to the said cable, and which is highly resistive to damage by high temperatures or corrosive fumes.
It is a further object of the present invention, to provide an automobile ignition cable assembly as aforementioned, which can be utilized in modern engines and with high voltage inputs, and yet generate relatively minute quantities of RF signals, thereby minimizing interference with radio and television receivers and/or with other communications equipment.